mimetype can't be None and always use filename if available

CHANGES.rst

@@ -4,6 +4,9 @@ Changelog
 1.5.9 (unreleased)
 ------------------
 
+- Make sure mimetype is not None and use use filename for detection if available.
+  [tschanzt]
+
 - Make sure the id is safe before setting the filename as id
   [pbauer]
 

src/plone/app/blob/field.py

@@ -234,13 +234,18 @@ def set(self, instance, value, **kwargs):
         blob = BlobWrapper(self.default_content_type)
         if isinstance(value, basestring):
             value = StringIO(value)     # simple strings cannot be adapted...
+            setattr(value, 'filename', kwargs.get('filename', None))
         if value is not None:
             blobbable = IBlobbable(value)
             try:
                 blobbable.feed(blob.getBlob())
             except ReuseBlob, exception:
                 blob.setBlob(exception.args[0])     # reuse the given blob
-            blob.setContentType(kwargs.get('mimetype', blobbable.mimetype()))
+            mimetype = kwargs.get('mimetype', None)
+            if not mimetype:
+                mimetype = blobbable.mimetype()
+            if mimetype and mimetype != 'None':
+                blob.setContentType(mimetype)
             blob.setFilename(kwargs.get('filename', blobbable.filename()))
         super(BlobField, self).set(instance, blob, **kwargs)
         # a transaction savepoint is created after setting the blob's value

src/plone/app/blob/tests/test_base_fields.py

@@ -7,7 +7,6 @@
 from plone.app.blob.field import FileField, ImageField
 from plone.app.blob.tests.utils import getFile
 
-
 SampleSchema = BaseSchema.copy() + Schema((
 
     FileField(
@@ -83,6 +82,20 @@ def testGetSize(self):
         field = item.getField('hmm')
         self.assertEqual(field.getSize(item), (0, 0))
 
+    def testSetFieldDefaultMime(self):
+        item = self.create()
+        file_ = getFile('test.pdf')
+        item.setFoo(file_, filename='file.blubb', mimetype=None)
+        self.assertEqual('application/pdf', item.getFoo().getContentType())
+
+    def testStringDataRespectsFilename(self):
+        item = self.create()
+        file_ = getFile('test.pdf')
+        item.setFoo(file_.read(), filename='file.xls', mimetype=None)
+        self.assertEqual(
+            'application/vnd.ms-excel',
+            item.getFoo().getContentType()
+            )
 
 def test_suite():
     from unittest import defaultTestLoader